The objective of the proposed research is to study mechanisms by which the permeability of the muscle postjunctional membrane is blocked (receptor desensitization) during application of selected quaternary ammonium compounds. Factors to be studied include the role of Ca, Ca ionophores and temperature variation on the kinetics of receptor desensitization. The work involves use of frog skeletal muscle fibers and application of various electrophysiological techniques such as point voltage clamping, iontophoresis, computer based modelling, etc.